Kitchen extract duct cleaning in hospitality

How often should kitchen extract cleaning take place?

Several sources give a direction. They differ in detail, but they say the same thing: the more intensively you cook, the more often.

Look at your own kitchen. A lunchroom with a toastie maker is in a different category from a snack bar with three fryers running from eleven in the morning to eleven at night. Also check your own policy: the conditions of your insurer take precedence. More on intervals in other buildings under how often should air ducts be cleaned.

When is a cooker hood duct too greasy? Measuring in microns

You cannot judge a duct by looking into the hood alone. KHN points out that serious contamination is often not visible to the naked eye. That is why grease is measured in micrometres (µm).

The quality mark scheme of the NVRL, the Dutch association of air handling system cleaning specialists, drawn up with TNO, works with two values:

• Intervention value 500 µm: above this grease layer you must clean.
• Performance value 200 µm: after cleaning, no more than this may remain.

Measurement is done with a wet film thickness gauge, with an accuracy of 20 µm. A sample is taken behind every extraction hood and per 10 metres of duct. The quality mark is valid for 1 year if the limit values are met.

According to trade publications, the new EN 15780:2025 also covers commercial kitchen extraction for the first time, with comparable grease thicknesses. For the text of the standard and the background, see NVRL quality mark.

What do insurers ask for when you clean an extract system?

Fire insurers require regular maintenance, and after a fire the loss adjuster wants to see that you have done it. KHN names three things that show your duct is clean: a report, photos and a certificate.

What belongs in the file

1. Date and scope of the cleaning: which hoods, which duct length, fan and motor.
2. Grease measurements before and after, per measuring point.
3. Photos of the same spots before and after.
4. Spots that were not accessible, with a proposal for an extra hatch.
5. A certificate or statement from whoever did the cleaning.

In its prevention conditions, Goudse also sets requirements for the ductwork: rigid, not flexible and not ribbed, made of aluminium or steel. A ribbed flexible hose holds on to grease and is hardly possible to clean. If you come across such a section, advise the client to replace it.

Why dry brushing in a commercial kitchen is not always enough

For ordinary supply and exhaust, dry methods are usually sufficient. The Eurovent recommendation on duct cleanliness, however, states that wet methods are needed for commercial kitchen exhaust. Grease is sticky and smears if you only go over it with a dry brush.

In practice you therefore work in stages: first grease filters and hood, then soak or spray the duct with a degreaser, then clean mechanically and extract. Danduct supplies a spraying system for the DC4, the DC4 Sprayer System. Ask Lamers whether it suits your cleaning agent and duct.

A useful habit for contractors: agree with the kitchen on a fixed moment for the work, after closing time, so the degreaser has time to soak in and the kitchen is dry and ready again before the next service.

Equipment for removing grease from kitchen extract ducts

A hospitality duct is often short, with sharp bends and a vertical section to the roof. That calls for a machine that can handle bends and a brush that loosens grease.

• The Electric duct brushing machine for cleaning contractors works in round and square ducts of 100 to 600 mm, goes vertical and through 90 degree bends and reaches up to 30 metres.
• For baked on grease there are more aggressive Tynex brushes. The page on duct cleaning brushes for cleaning contractors explains which brush suits which kind of contamination.
• With compressed air duct cleaning for cleaning contractors you look inside the duct via the camera. Useful for seeing beforehand where the grease is and showing afterwards that it has gone.

For a comparison of all kits, also for those who do several kitchens a week, look at duct cleaning kit for cleaning contractors.

Fictitious example: a grill restaurant after the insurance inspection

After an inspection by its insurer, a grill restaurant is asked for a cleaning report for the extract duct. There is none: the grease filters are washed weekly, but the duct has never been cleaned.

A camera inspection shows that the vertical section just behind the hood is the greasiest. That is where grease condenses first, because the air cools down. Further along the duct the layer is thinner. After cleaning, the report shows the before and after value per measuring point, with photos. From now on the owner schedules two cleans a year, because the grill runs for long hours every day.

What you learn from this: washing filters weekly is necessary, but it does not replace duct cleaning. Hotels with their own restaurant kitchen face the same question; see air duct cleaning in hotels. To find out what such a job typically costs, look at air duct cleaning prices.

A short checklist you can hand to a restaurant client: weekly filter washing logged, yearly duct inspection booked, report with grease values and photos filed with the insurance papers, and any flexible ribbed sections flagged for replacement.